A method for filling a conventional gas-filling packaging machine with an inert gas is disclosed in JP-A-2004-67224 by the present applicant. The gas-filling packaging machine is constructed so that a single intermittently rotating table is used for filling a packaging bag with articles, filling an inert gas such as nitrogen gas and heat-sealing a top of the bag after the bag has been filled with the articles and inert gas. A nozzle for filling with the inert gas is constructed so as to be fixed to an outer surface of a filling funnel provided on a packaging bag the top of which is open. The filling funnel has a discharge hole which rises and sets relative to the packaging bag.
The nozzle for filling the packaging bag with the inert gas employs such a structure as to be fixed to the outer surface of the filling funnel as described in the foregoing gazette or such a structure as to be fixed to a central inside of the filling tunnel. However, a distal end of the nozzle is inserted into a corner of the packaging bag in the former fixing structure. Accordingly, when the packaging bag is a flat bag or a packaging gusset bag e as shown in FIG. 8, the distal end of the nozzle tends to be easily detached from the top of the bag. Furthermore, FIG. 9 shows a chuck bag a with side gusset. The chuck bag a has both sides with folds c respectively. There is a rare defect that the distal end of the nozzle n sticks into inwardly extending parts of the folds c.
In the latter nozzle fixing structure, the nozzle fixed to the central inside of the filling funnel constitutes a barrier to the article passing, resulting in an increase in the filling time. As a result, the filling funnel is clogged by the article in some cases.
Furthermore, in the inert gas filling method described in the above gazette, gas replacement is not carried out while the top of the bag is closed. Accordingly, gas replacement is sometimes unfavorable depending upon a type or size of a packaging bag or a type of the article.    Patent Document: JP-A-2004-67224